1. Technical Field
The present invention relates generally to vehicle adaptive cruise control systems, and more particularly to a method and apparatus for adjusting vehicle speed and inhibiting vehicle resume speed in response to object detection and road curvature.
2. Background of the Invention
Adaptive Cruise Control (ACC) has reached a level of technical and business readiness such that it is beginning to appear in the consumer market as a comfort and convenience system. Consumer technical enthusiasm for ACC has increased because of their interest in intelligent vehicles and systems such as collision warning and collision avoidance. ACC performs as an enhancement to traditional cruise control by automatically adjusting a set speed, which is set by the vehicle operator, to allow a vehicle to adapt to moving traffic.
Under normal driving conditions the ACC system is engaged with a set speed equal to a maximum autonomous speed that is desired by the operator and the ACC system operates in a conventional cruise control mode. When the vehicle approaches traffic, the ACC system automatically adjusts the set speed to follow the traffic at a desired headway distance. When the traffic clears or the vehicle changes lanes the ACC system slowly resumes the speed of the vehicle to the set speed. When the vehicle approaches slow traffic the ACC system is automatically disengaged and the operator manually follows slower vehicles in the slow traffic. When the slow traffic is no longer in front of the vehicle the operator pushes the resume button and the ACC system accelerates the vehicle back to the set speed.
Current ACC systems are unable to reliably classify stopped objects to the degree necessary to actively cause a vehicle to brake in the presence of stopped objects. The stopped objects may be impending when the vehicle is passing a target vehicle or when the vehicle is changing lanes. The current ACC system therefore relies on the operator to stop the vehicle. The stopped object may be another vehicle or some other object. Objects such as bridges, signs, guardrails, and construction barrels that overhang or are near a road edge are also not detected by the ACC system. Since, the ACC system does not detect stopped objects the ACC system may interpret the stopped object as though the road in front of the vehicle is clear and attempt to attain the resume speed. Just as in any cruise control system driver intervention may be required.
As may be expected path prediction of traditional ACC systems generally classifies close objects, less than 50 meters, very well during normal driving conditions in which road curvature is very slow such as highway type roads. However, as the range increases beyond 90 to 100 meters fundamental assumptions of the yaw rate prediction become less statistically valid and may result in misclassifications. As the operated vehicle is following a target vehicle the ACC system radar field may not be continuously directed at the target vehicle, therefore not detecting the target vehicle and begin to accelerate the vehicle. Also “driver hunting” as in transitional maneuvers such as in lane changes and entry and exit conditions become more pronounced. Misclassifying objects is more evident with roadside clutter, which can cause the ACC system to interpret the roadside clutter as in-path targets at longer ranges.
Traditional ACC systems were designed to only react to moving targets presented by normal traffic under extended cruise control operation, thereby, compromising the goals of a collision warning or avoidance system. The current statistical nature of the path prediction in ACC systems can potentially be annoying to the operator of the vehicle by alerting the operator in unnecessary conditions and applying vehicle brakes or accelerating the vehicle in unwarranted situations.
It would therefore be desirable to develop an ACC system that correctly classifies stopped objects. It would also be desirable for the ACC system to correctly classify objects during operation on a curved road. Correctly classifying objects in various road conditions may increase the success of ACC systems in the consumer market and also increase the collision warning capabilities of a vehicle.